TRAVERSE CITY, Mich. (AP) — If huge, hungry Asian carp reach Lake Michigan,
their long-dreaded invasion may turn out to be less ferocious than once
expected because a tiny competitor is gobbling up their primary food source,
some Great Lakes researchers say.
The quagga mussel, a thumbnail-sized foreign mullosk first spotted in the
lakes two decades ago, has devoured so much plankton in southern Lake
Michigan that the entire food web is being altered, federal and university
scientists reported in a series of newly published articles.
Mussels have “beaten the Asian carp to the buffet table,” Gary Fahnenstiel,
senior ecologist with NOAA’s Great Lakes Environmen-tal Research Laboratory,
said Tuesday. “While the public has been worried about Asian carp and the
Chicago canal, another invader has fundamentally changed the lake and made
it inhospitable to the Asian carp.”
Some biologists and government officials say if the carp get a foothold in
Lake Michigan, they could spread to most of the Great Lakes and vacuum up
enough plankton to threaten collapse of the $7 billion fishery. But
Fahnenstiel and other researchers said the quagga mussel is a greater
Some types of microscopic plants have declined more than 80 percent with the
mussel’s arrival, they said, which probably explains a similar drop-off of a
freshwater shrimp species that is a dietary staple for small fish pursued by
prized sport varieties such as salmon and trout.
Other scientists and policymakers insisted the carp could survive and even
thrive in a plankton-depleted environment.
“They can eat other things besides plankton,” said Duane Chapman, a U.S.
Geological Survey fisheries biologist. “They are very flexible fish.”
Bighead and silver carp — Asian varieties threatening to enter Lake Michigan
through Chicago-area rivers and canals — are filter feeders that consume up
to 40 percent of their body weight daily. The biggest can grow to 4 feet in
length and weigh 100 pounds.
But Fahnenstiel said that if carp evade electronic barriers and reach the
lake, they’ll probably find so little nourishment they’ll either go back or
Chapman is based at the Columbia Environmental Research Center in Missouri,
where researchers are measuring Asian carp’s appetite for substances that
will remain abundant in the Great Lakes even where plankton runs short. One
example: bits of food the mussels spit out rather than digest.
Another is cladophora, a green algae that annoys beachgoers by washing
ashore in stinky, rotting clumps. The cause of its resurgence in recent
years is unknown but some believe it’s linked to the mussels, which improve
clarity as they filter water, allowing sunlight to penetrate deeper.
“Chances are pretty good that Asian carp would do just fine eating that
stuff, but we’re going to test it to make sure,” Chapman said.
Quagga and zebra mussels, believed to have hitched a ride from Europe to the
Great Lakes in ballast tanks of freighter ships in the 1980s, have wreaked
ecological havoc and done hundreds of millions in damage to all the lakes
except Superior, where only isolated colonies have been found.
Fahnenstiel and Michigan Tech University biologist Charles Kerfoot were
among co-authors of a series in the Journal of Great Lakes Research that
described the quagga mussel’s takeover of southern Lake Michigan this
Quaggas — which unlike zebra mussels thrive in cold, deep waters — are a
likely culprit in the disappearance of phytoplankton blooms that feed
opossum shrimp, the scientists said.
Those tiny invertebrates, crucial food for prey fish, have plummeted by more
than 70 percent, said Steve Pothoven, a biologist with the National Oceanic
and Atmospheric Administration field station in Muskegon.
Scientists say whitefish and salmon, two of Lake Michigan’s most popular
species, have gotten smaller in recent years, a probable sign of
malnutrition from a deteriorating food web.
“We are really getting a genuine collapse in the third-largest freshwater
lake in the world,” Kerfoot said.
The quagga population should outgrow its food supply and level off sometime.
How soon that happens will determine how severely fish populations suffer,
Tom Nalepa, another NOAA researcher.
If Asian carp arrive in large numbers and successfully reproduce, the
situation would get even more dire.
Even as scientists debate how likely that is, five Great Lakes states are
suing in federal court, demanding closure of Chicago shipping locks and
separation of the lakes from the Mississippi River basin to block the path
of Asian carp and other invaders. Chicago business interests say doing so
would cripple the local economy.
Marc Gaden, spokesman for the Great Lakes Fishery Commission, says he hopes
never to find out how well the carp would fare in Lake Michigan.
“What’s important is to focus on the prevention,” Gaden said. “Once you let
the invaders in and they spread, it’s permanent.”
On the Net:
Journal of Great Lakes Research,